Plasticizing additives are used in plastics and elastomers to achieve various effects. Such plasticizers may improve melt processing characteristics or may modify physical properties of the polymer under use conditions, or both.
Highly fluorinated polymers have desirable combinations of electrical, chemical, and thermal properties. However, the high molecular weight required to realize the properties necessary for severe service conditions can make fluoropolymers difficult to process. Tetrafluoroethylene (TFE) homopolymers are so intractable that conventional melt processing techniques cannot be used and articles are fabricated by methods adapted from powder metallurgy. Partially-crystalline copolymers of TFE with other fluorinated monomers are melt-fabricable but processing rates are limited, especially for grades designated for the most severe service. Likewise, the rates at which fluoroelastomers, both vinylidene fluoride (VF.sub.2) copolymers and perfluoroelastomers, can be shaped are limited. In addition, the accessible balance of properties for fluoroelastomers is unsatisfactory for some uses, a softer or less stiff compound frequently being desired.
U.S. Pat. No. 3,665,067 discloses the use of hexafluorobenzene as a plasticizer for polytetrafluoroethylene (PTFE) in the fabrication process known as ram extrusion. U.S. Pat. No. 4,012,453 discloses the use of chlorofluorinated aromatic hydrocarbons as plasticizers for trifluorochloroethylene polymers.
U.S. Pat. No. 2,510,078 discloses the use of fluorinated oils as plasticizers for certain fluoroplastics including PTFE. U.S. Pat. No. 3,434,996 discloses the use of chlorofluorinated ethanes as extrusion lubricants for PTFE to overcome the deleterious effect on properties of oils, greases, and waxes when used as plasticizers. U.S. Pat. No. 3,030,328 discloses a copolymer of TFE and a fluorinated alpha-olefin plasticized with esters of fluoroalcohols with cyclic polycarboxylic acids to improve melt flow and toughness.
U.S. Pat. No. 3,069,401 discloses the use of VF.sub.2 /HFP copolymer greases in VF.sub.2 /HFP fluoroelastomers to change viscosity without altering the properities of the cured elastomer. Since the chemical compositions of the grease and the fluoroelastomer are similar, this appears to be equivalent to modifying the molecular weight distribution of the fluoroelastomer. U.S. Pat. No. 4,810,765 teaches the use of cotelomers of VF.sub.2 which can participate in peroxide curing of fluoroelastomers. U.S. Pat. No. 3,804,801 discloses the use of a modified fluorosilicone polymer in a fluoroelastomer to improve low-temperature properties.
It is also known to use fluorinated polyethers as plasticizers for hydrogen-containing fluoroelastomers and perfluoroelastomers, as taught in by U.S. Pat. Nos. 4,413,094; 4,894,418; and 5,061,759. However, the polyethers have limited compatibility with the fluoropolymers and will exude at moderate concentrations unless modified to participate in the curing reaction.